1. Field of the Invention
The present invention relates to a RAKE combiner apparatus using a charge transfer element, which is used in a path diversity receiver in a CDMA (Code Division Multiple Access) communication.
2. Description of the Related Art
The path diversity reception technology becomes important technical means which is inevitable today in mobile communication apparatuses that are used in multifarious communication environments.
The RAKE system, one of such technical means, is currently at the practical phase due to the recent improvement on the performance of digital signal processing. In the mobile communication field which has some restrictions on the equipment size and power supply, however, attempts to put the system to a practical use are still being made.
That is, there are the following problems to which optimal solutions have not been found yet. First, in digitizing all the processes in the base band as shown in FIGS. 7 and 8, while a more ideal system can be constructed, A/D conversion and matched filtering requires great power. Secondly, in a case where a matched filter is constituted of an analog circuit as shown in FIGS. 9 and 10, while power consumption approaches a practical level, new restrictions on the length of matching codes or the like may come up due to the precision of the analog circuit.
In either case, as the xe2x80x9cnumber of fingersxe2x80x9d that greatly affects improvement on the performance of the RAKE process leads to system complication, as many as about four fingers are merely used.
One solution to the above problem is a xe2x80x9cmatched filter acting in charge domainxe2x80x9d which is disclosed in Japanese Patent No. 2773075 (corresponding to U.S. patent application Ser. Nos. 08/997,848) and 09/064,751, filed by the same applicant as that of the present invention. As shown in FIG. 11, this device receives an input potential signal and sequentially outputs a train of charge packets which indicate a correlation with a predetermined matching code.
Accordingly, it is an object of the present invention to provide a RAKE combiner apparatus using a charge transfer element, which can permit a high-precision RAKE receiver to be constructed by a simple circuit structure that merely performs selective accumulation of the output charges, has very few active elements, resulting in lower consumption power, can allow the finger number to be arbitrarily set within a range of up to the number of taps of the matched filter and can implement a highly efficient RAKE process.
To achieve this object, according to this invention, a RAKE combiner apparatus using a charge transfer element, comprises at least one charge routing mechanism for receiving a group of charge signals in at least one time sequence, and transferring each of the input charge signals to at least two different kinds of routes in accordance with a separately supplied digital signal; at least one signal accumulation mechanism for executing signal accumulation by integrating the routed charge signals directly as charges or after subjecting the routed charge signals to predetermined signal conversion; and a RAKE controller for predicting a multi-path environment of communication paths associated with reception of the input charge signals, and supplying a digital signal for determining a transfer route of each of the input charge signals to the charge routing mechanism.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.